The use of electronic stimulation systems to control pain by nerve or muscle stimulation has been in use for a number of years. For example, spinal cord stimulation (SCS) is a technique that has been used for pain management since the 1960s. SCS systems generally feature a pulse generator coupled to one or more percutaneous leads having a plurality of electrodes disposed in an area in which neurostimulation is desired.
The pulse generator may be provided in various configurations, such as a totally implanted pulse generator (IPG) or a radio frequency (RF) system. A typical IPG configuration comprises a surgically implanted, internally-powered pulse generator and multi-electrode lead. A typical RF system configuration comprises a surgically implanted, passive receiver and a transmitter which is worn externally. In operation, the transmitter communicates, through an RF signal, to the implanted receiver to provide stimulation energy and control.
The leads used with any of the foregoing pulse generators may be positioned within a patient's epidural space, typically parallel to the axis of the spinal cord. The electrodes are used to deliver a particularized electric field to a specific region of the spinal cord or surrounding tissue. Applying an electric field across one or more nerve bundles and/or nerve roots can produce paresthesia, or a subjective sensation of numbness, tingling or “pins and needles,” at the affected nerves' dermatomes. This paresthesia, if properly directed and produced at the necessary levels, can “mask” certain forms of chronic pain.
Implantation of a pulse generator, whether a fully implanted IPG or a RF system receiver/transmitter, necessarily requires a neurostimulation patient to undergo an implantation surgery. Additionally, routing a lead subdermally between an implanted pulse generator and the tissue area to be stimulated typically requires a relatively invasive procedure, such as a tunneling procedure. However, a lead having electrodes thereon suitable for providing neurostimulation when coupled to a pulse generator may be implanted through much less invasive means, such as through a laparoscopic needle procedure.
The focus, characteristics and intensity of the generated electric field are determined by the electrode configuration (i.e., the polarity, if any, assumed by each electrode) and the electric pulse waveform (collectively “stimulation setting”). The waveform properties include, at least, a stimulation frequency, a stimulation pulse width and phase information.
Accordingly, a physician, nurse, or clinician (referred to collectively herein as clinician) may advantageously couple a pulse generator to a lead or leads in the course of performing a lead and/or generator implantation procedure on a patient in order to confirm proper operation of neurostimulation. For example, a clinician may couple a pulse generator to a lead during a lead implantation procedure to confirm the electrodes are disposed at a proper location within the patient. Similarly, prior to implantation of a pulse generator, a clinician may couple a pulse generator to a lead to determine the stimulation setting to implement in the implanted pulse generator in order to achieve the desired results.
Additionally or alternatively, a patient may wish to experience neurostimulation for a period of time, before undergoing procedures for implanting a pulse generator and subdermally coupling a lead thereto, in order to determine if the feeling associated with paresthesia is acceptable to the patient and that the therapy acceptably masks the patient's pain. Accordingly, a lead or leads (perhaps “trial” leads to be removed and subsequently replaced with “permanent” leads upon successful conclusion of a trial period) may be laparoscopically or surgically inserted, with an end distal to the electrodes left external for coupling to a pulse generator. With a suitable pulse generator coupled to the lead, the patient may experience the prescribed neurostimulation therapy for a trial period, e.g., several hours to 30 days, to determine if the therapy is satisfactory before undergoing implantation procedures.
Various forms of pulse generators have been provided in configurations adapted for the foregoing trial uses (such pulse generators being referred to herein as “trial stimulators”). These trial stimulators have typically been relatively limited in their functionality and features. For example, trial stimulators available today provide for connection to either 4, 8, or 16 electrodes and no more.
Generally, the same trial stimulator configuration is used whether the patient or the clinician is conducting the trial, although a patient may be restricted from accessing certain features of the trial stimulator. For example, a micro-switch bank may be provided to allow a clinician to select stimulation pulse widths and amplitudes, with a cover being provided to prevent a patient from accessing the micro-switch bank during their trial period. Additionally or alternatively, a lockout switch or mechanism may be implemented to prevent a patient having physical access to particular control means, such as the aforementioned micro-switch bank, from altering particular operational aspects of the trail stimulator.
The foregoing trial stimulators do not present an interface which is equally easy to use in the various situations they are expected to be used in, e.g., interoperatively in the operating room and patient trial. For example, where features or functions are provided for ready access when used interoperatively, such as to provide complex control alternatives for establishing a precisely tailored stimulation program, the trial stimulator is typically not well suited for use by the patient. Likewise, where relatively simple and intuitive features or functions are provided for simplified access during a patient trial, such as to facilitate a patient manipulating a relatively complex stimulation program to experience various stimulation parameters in a home trial, the trial stimulator is typically not well suited for use by the clinician.
Trial stimulators that have been provided in the past have generally delivered constant voltage pulses to the lead electrodes. Traditional wisdom has been that by delivering constant voltage, if an electrode should fail (e.g., become disconnected from the stimulator) the voltage to the system would remain unchanged, thus having no change on battery life and presenting little risk of over stimulation because the voltage to the remaining electrodes would remain substantially unchanged.
Although providing some form of real-time variable stimulation, the trial stimulators available today do not provide true continuous multi-stimulation programs. By multi-stimulation programs, it is meant that a first set of stimulation parameters (e.g., amplitude, pulse width, frequency, and electrodes) are implemented to provide a first desired therapy (e.g., relieve pain associated with a first portion of the body) and a second set of stimulation parameters are implemented to provide a second therapy (e.g., relieve pain associated with a second portion of the body). Multi-stimulation programs of prior trial stimulators have implemented each stimulation parameter set for a predetermined period of time (multiple stimulation pulses) before moving to a next stimulation parameter set. Even where a few different stimulation program sets are used, e.g., 3, the cycle time for the trial stimulator returning to the first stimulation program set may be high. Patients have stated that such a periodic cycling of stimulator parameter sets sometimes results the patient being able to feel the stimulation cycles as a “fluttering” which, although not particularly unpleasant, is noticeable.
Another attempt at providing a patient with multiple stimulation programs using a trial stimulator has been to implement dual stimulation. For example, a trial stimulator having 8 channels may be provide a first stimulation parameter set to 4 electrodes while providing a second stimulation program parameter set to a different 4 electrodes.